The liquefaction of natural gas is gaining in importance as raw materials become scarce and there is increasing environmental awareness. In many cases, natural gas represents a more environmentally friendly, safer and sometimes more readily available alternative to other sources of energy. However, gas has the disadvantage that transportation and storage can be very costly, and can be carried out more expediently in the liquid state. Accordingly, installations for liquefying natural gas are also gaining in importance.
Conventional installations for liquefying natural gas usually comprise one or two compressors or compressor casings that are driven by at least one gas turbine or a motor. These liquefied natural gas installations with a high annual production (5 to 10 MPTA) normally use what are known as single-shaft gas turbines, in which the gas turbine compressor and the turbine of the gas turbine are located on a shaft assembly. These single-shaft gas turbines are not capable of starting independently or starting at nominal speed, and to do so often require a starter-helper motor. This starter-helper motor is often also used for supporting the gas turbine when there are high power requirements. The operation of this motor requires high-voltage power electronics, which are designed for power outputs of approximately 40 MW in a relatively large installation.